The present invention relates to a cooking appliance such as a microwave oven.
In the conventional microwave oven, completion of cooking is detected when that gas or moisture produced by cooked food in a heating chamber is detected by a detecting device when the surface temperature of the food to be cooked is detected by an infrared light detector, or when the temperature of exhaust air from the heating chamber is detected by a thermistor. When a predetermined condition such as the completion of food to be cooked is detected, the induction heating device is stopped.
In the conventional cooking techniques, if power is applied to a magnetron for producing a high frequency when food to be cooked is absent from the heating chamber, referred to as no-load condition, the gas or the moisture is not produced in the heating chamber. Accordingly, in the microwave oven in which the cooking completion of the food is judged by detecting the gas or the moisture from cooked food, the heating operation is continuously carried out. Further, a temperature of the heating chamber is locally and highly increased, so that use of the cooking appliance becomes dangerous.
In the microwave oven including an infrared light detecting device or a thermistor, when the food to be cooked is absent from the heating chamber, the heating operation is continuously carried out until the temperature in the heating chamber reaches a predetermined temperature. As the heating chamber is usually made of a metal material for reflecting microwaves, an increase of the temperature in the heating chamber is small as compared with the increase of the temperature of food which easily absorbs a high frequency signal and has a high dielectric constant. Accordingly, the heating period, even in the no-load condition, will continue for a long time.
Accordingly, that an improved cooking apparatus such as a microwave oven is disclosed, which can detect whether food to be cooked is present or absent in the heating chamber and enables a heating operation for a short period of time even when the food to be cooked is absent or just a small amount of the food to be cooked is present in the heating chamber.